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JSON Schema Validation with Play JSON
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It is a stupid thing, but in your example are using a different constructor and the builder need a Lang implicitly. 

Anyway, It is an awesome library
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README.md

Play JSON Schema Validator

Build Status Coverage Status

This is a JSON schema (draft v4/draft v7) validation library for Scala based on Play's JSON library.

If you experience any issues or have feature requests etc., please don't hesitate to file an issue. Thanks!

Installation

Add an additional resolver to your build.sbt file:

resolvers += "emueller-bintray" at "http://dl.bintray.com/emueller/maven"

Then add the dependency:

libraryDependencies += "com.eclipsesource"  %% "play-json-schema-validator" % "0.9.5-M4"

Please also see the respective release notes.

Usage

Schemas can be parsed by passing the schema string to Json.fromJson. Starting with 0.9.5 (which adds draft 7 support), Reads and Writes have become version specific, hence you need to import them via respective Version object:

  import Version7._ // since 0.9.5 necessary
  val schema = Json.fromJson[SchemaType](Json.parse(
    """{
      |"properties": {
      |  "$id":    { "type": "integer" },
      |  "title": { "type": "string" },
      |  "body":  { "type": "string" }
      |}
    }""".stripMargin)).get

With a schema at hand, we can now validate JsValues via the SchemaValidator:

val validator = SchemaValidator(Some(Version7))
validator.validate(schema, json)

validate returns a JsResult[A]. JsResult can either be a JsSuccess or a JsError. validate is also provided with overloaded alternatives where Play's Reads or Writes instances can be passed additionally. This is useful for mapping JsValues onto case classes and vice versa:

validate[A](schemaUrl: URL, input: => JsValue, reads: Reads[A]) : JsResult[A]
validate[A](schemaUrl: URL, input: A, writes: Writes[A]): JsResult[JsValue] 
validate[A: Format](schemaUrl: URL, input: A): JsResult[A] 

Error Reporting

In case the validate method returns an failure, errors can be converted to JSON by calling the toJson method. Below is given an example taken from the example app:

import com.eclipsesource.schema._ // brings toJson into scope

val result = validator.validate(schema, json, Post.reads)
result.fold(
  invalid = { errors =>  BadRequest(errors.toJson) },
  valid = { post => ... } 
)

Errors feature a schemaPath, an instancePath, a value and a msgs property. While schemaPath and instancePath should be self explanatory, value holds the validated value and msgs holds all errors related to the validated value. The value of the msgs property is always an array. Below is an example, again taken from the example app.

{
  "schemaPath" : "#/properties/title",
  "keyword": "minLength",
  "instancePath" : "/title",
  "value" : "a",
  "msgs" : [ "a violates min length of 3", "a does not match pattern ^[A-Z].*" ],
  "errors": []
}

The value of schemaPath will be updated when following any refs, hence when validating

{
  "properties": {
    "foo": {"type": "integer"},
    "bar": {"$ref": "#/properties/foo"}
  }
}

the generated error report's schemaPath property will point to #/properties/foo.

id

In case the schema to validate against makes use of the id property to alter resolution scope (or if the schema has been loaded via an URL), the error report also contains a resolutionScope property.

anyOf, oneOf, allOf

In case of allOf, anyOf and oneOf, the errors array property holds the actual sub errors. For instance, if we have a schema like the following:

{
  "anyOf": [
    { "type": "integer" },
    { "minimum": 2      }
  ]
}

and we validate the value 1.5, the toJson method returns this error:

[ {
  "schemaPath" : "#",
  "errors" : {
    "/anyOf/0" : [ {
      "schemaPath" : "#/anyOf/0",
      "errors" : { },
      "msgs" : [ "Wrong type. Expected integer, was number" ],
      "value" : 1.5,
      "instancePath" : "/"
    } ],
    "/anyOf/1" : [ {
      "schemaPath" : "#/anyOf/1",
      "errors" : { },
      "msgs" : [ "minimum violated: 1.5 is less than 2" ],
      "value" : 1.5,
      "instancePath" : "/"
    } ]
  },
  "msgs" : [ "Instance does not match any of the schemas" ],
  "value" : 1.5,
  "instancePath" : "/"
} ]

Customizable error reporting

The validator allows you to alter error messages via scala-i18n, e.g. for localizing errors reports. You can alter messages by placing a messages_XX.txt into your resources folder (by default conf). The keys used for replacing messages can be found here. In case you use the validator within a Play application, you'll need to convert Play's Lang and make it implicitly available for the SchemaValidator, e.g. via:

implicit def fromPlayLang(lang: Lang): com.osinka.i18n.Lang = com.osinka.i18n.Lang(lang.locale)

Example

An online demo of the library can be found here.

See the respective github repo for the source code.

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